British children are being dosed with slimming drugs intended as a last resort for severely obese adults, underlining the desperate measures being taken by parents of overweight youngsters.

The treatment, Xenical, is not even licensed for children because there have been no trials of how it affects growing bodies. Official guidance is that it should be reserved for adults alone.

Yet a startling 3,000 prescriptions for orlistat, commercially known as Xenical - which can cause unpleasant side effects, including stomach cramps and diarrhoea - were issued to children last year, a revelation which will prompt fresh debate over how to tackle the growing epidemic of childhood obesity.

Dr Nick Finer, a leading obesity specialist, said the figures were 'surprisingly' high but reflected the seriousness of the problem. Doctors were now seeing 15-year-olds who had been overweight for a decade and were at clear risk of developing potentially life-threatening diabetes as a result.

'What would really disturb me is if any of those 3,000 were children going into their GP with their parents and the parents saying, "My child is fat, can you do something?" and going out with a prescription for orlistat and nothing else,' said Dr Finer, a consultant in obesity medicine at Addenbrooke's hospital in Cambridge.

'But if there are children who are at high risk, who have tried and failed simple lifestyle interventions, I am not sure that a doctor isn't put in a moral dilemma.'

Dr Finer said he had 'once or twice' given Xenical to teenagers between 16 and 18, including one so overweight they were suffering breathing difficulties in their sleep.

The Liberal Democrat MP Paul Marsden, who obtained the figures from Health Minister Melanie Johnson, warned that parents could be demanding the drug for the wrong reasons.

'These figures may demonstrate that the problem of obesity in children is getting out of hand, but is this the best way of treating it?' he said.

Fierce debate over childhood obesity was triggered last year by news that an 11-year-old girl, weighing 20 stone, faced a stomach stapling operation.

British doctors refused to operate on Gemma Taylor for another five or six years, until she had stopped growing. Among younger children, a key problem was parents 'abrogating' their responsibility to insist on a healthy diet, Finer said.

'They will say "I have to cook chips because that's what the children want", and I say, "They might want it but they don't need it".'

More than one in seven children aged between six and 15 is now obese: the Department of Health has calculated that obesity in the UK will rise by up to 50 per cent from 1998 levels by 2010.